Cell migration and cell-substratum interaction underly numerous morphogenetic processes. These activities affect many developmental abnormalities, as well as play a role in tumor metastasis. The overall objective of the proposed studies is to identify the cell-substratum interactions which are required for the onset and termination of cell migration in situ. The primary mesenchyme cells of the sea urchin embryo of Lytechinus pictus and Strongylocentrotus purpuratus will be used as a model system for these studies because cell migration can be readily observed and manipulated in situ. The proposed work will focus on components of the migratory substratum present in the blastocoel. The role of these components in cell migration will be studied by timelapse cinematography and scanning and transmission electron microscopy in normal or in sulfate-deprived and Beta-D-xyloside treated embryos in which cell migration does not occur. The functionally important macromolecules of the blastocoel will be characterized by gel chromatography, acrylamide gel electrophoresis, and lectin affinity chromatography. Finally, the effects of some of these matrix components on cell attachment and migration will be examined on normal and reconstituted matrix isolated from the blastocoels of normal and treated embryos.